The effects of lunar phase on wildlife behavior--and that of human beings--are, for the most part, poorly understood. As the moon rotates around the Earth, its position relative to the planet and to the Sun shift, as does its appearance to terrestrial viewers: it wanes and waxes between "new" and "full" phases, where it is completely shadowed and illuminated, respectively. The two half-moons in between are the first and last quarters. Fishermen are keenly interested in any potential relationship between the moon and their success out on the lake, creek or ocean.
Scientists have documented definite associations between the behavior of certain fish species and the Moon's cycle. In a paper on the detection of lunar cycles in ocean ecosystems, for example, researchers out of Montreal's McGill University noted that previous studies have shown that a number of fish spawn in concordance with the Moon's phase--especially those fish which reproduce in shallow waters that are heavily impacted by tides. Indeed, at least four orders of fish are considered lunar-synchronized spawners, according to a 1984 review in the Transactions of the American Fisheries Society by Malcolm H. Taylor.
Establishing a relationship between two phenomena like lunar aspect and fish behavior can be nearly impossible to do with absolute certainty. Beyond the scientific literature, the long-term, keen-eyed records of fishermen offer anecdotal but potentially illuminating insights. A survey of walleye fishermen, conducted by the Hunting and Fishing Library, revealed that the majority who fished on high-clarity lakes believed daytime fishing was best, and nighttime fishing worst when the Moon was full; the opposite impression was connected with the new Moon. Most fishers on low-clarity lakes tended to believe the reverse: night fishing was best and daytime fishing worst around the full Moon; and worst and best, respectively, around the new Moon. Also, the majority of respondents believed immediate weather patterns could negate any lunar influence. A similar survey of 200 smallmouth bass fishermen, reported in Steve Hauge's "Big Book of Bass," suggested that bass-fishing was best around the full and first-quarter Moons, and worst at the last-quarter.
The most predictable effect of lunar phase on fishing likely has to do with the tides, which are primarily caused by the gravitational pull of the Moon. The highest tides coincide with near and full Moon periods, which may result in more turbulent water less conducive to fishing. Fishers may find better luck plying the smaller, calmer tides of first- and last-quarter Moons. Bone up on the movement patterns of both bait- and gamefish during the various tidal stages--the ebb and flow of incoming and outgoing tides, and the extremes of high and low tides.
Other Moon Effects
In an article for "Angler Guide", Joe Bucher asserts that fish are most active around sunrise, sunset, moonrise and moonset--a temporal pattern possibly more definite than those associated with particular lunar phase.